1. Field of Invention
The present invention relates to a wavelength division multiplex optical star coupler, a communication station, and an optical transmission system. In particular, the present invention relates to an optical transmission system that uses a wavelength division multiplex optical star coupler which combines an optical star coupler and a wavelength division multiplex optical coupler.
2. Description of Related Art
An optical fiber communication using an optical fiber as a light propagation line will be described as a conventional art. Usually, an optical star coupler of 1 to n branching is used for dividing an optical signal, which is generated from one source, into a plurality of signals. Here, n is an integer more than 2. It is possible to transmit the same optical signal to a plurality of multiple destinations by the optical star coupler. An optical fiber fusion type and an optical waveguide type are mainly used for the optical star coupler. The optical star coupler is not only used for distributing the light, but also used as a light multiplexer which multiplexes the optical signal output from different light sources because the optical star coupler usually works bidirectionally.
One of methods to use a single optical fiber efficiently is a wavelength division multiplex method that utilizes different wavelengths of the optical signals. Recently, a wavelength division multiplex optical coupler is used for multiplexing or de-multiplexing the optical signals having different wavelengths in the wavelength division multiplex method.
FIG. 1 shows a conventional wavelength division multiplex optical coupler. The wavelength division multiplex optical coupler 10 is basically the same as a 1 to 2 optical de-multiplexer or multiplexer. One side of the wavelength division multiplex optical coupler 10 is connected to a port P20, which can input and output the first optical signal xcex1 and the second optical signal xcex2. The other side of the wavelength division multiplex optical coupler 10 is connected to a port P22, which can input and output only the first optical signal xcex1, and a port P24, which can input and output only the second optical signal xcex2.
The first optical signal xcex1 and the second optical signal xcex2 have different wavelength with each other. The first optical signal xcex1 input from the port P20 is output to the port P22, and the second optical signal xcex2 input from the port P20 is output to the port P24. The first optical signal xcex1 input from the port P22 and the second optical signal xcex2 input from the port P24 are output to the port P20. The ordinary wavelength division multiplex optical coupler is described in Japanese Patent Application Laid-Open No. H10-173265.
FIG. 2 shows a one-way direction wavelength division multiplex optical communication realized by the wavelength division multiplex method. One side of the wavelength division multiplex optical coupler 10 is connected to a port P26, which can input only the first optical signal xcex1, and a port P28, which can input only the second optical signal xcex2. The other side of the wavelength division multiplex optical coupler 10 is connected to the port P30, which can input the first optical signal xcex1 and the second optical signal xcex2. The first optical signal xcex1 input from the port P26 and the second optical signal xcex2 input from the port P28 are output to the port 30 through the wavelength division multiplex optical coupler 10. The direction of the communication is one-way from the port P26 and the port P28 to the port 30.
FIG. 3 shows a two-way direction wavelength division multiplex optical communication realized by the wavelength division multiplex method. One side of a wavelength division multiplex optical coupler 10a is connected to a port P32, which can input only the first optical signal xcex1, and a port P34, which can output only the second optical signal xcex2. The other side of the wavelength division multiplex optical coupler 10a is connected to a wavelength division multiplex optical coupler 10b. 
One side of the wavelength division multiplex optical coupler 10b is connected to a port P36, which can input only the second optical signal xcex2, and a port P38, which can output only the first optical signal xcex1. The other side of the wavelength division multiplex optical coupler 10b is connected to the wavelength division multiplex optical coupler 10a. The wavelength division multiplex optical coupler 10a and 10b are connected by a single optical fiber.
The first optical signal xcex1 input from the port P32 is output to the port P38 through the wavelength division multiplex optical couplers 10a and 10b. The second optical signal xcex2 input from the port P36 is output to the port P34 through the wavelength division multiplex optical couplers 10a and 10b. The direction of the communication is bidirection from the port P32 to the port P38 and from the port P36 to the port P34.
Therefore, the optical communication that transmits an optical signal from one light source, such as a main unit, to a plurality of receiving terminals, such as sub units, and transmits the optical signals from the sub units to the main unit become possible by using the wavelength division multiplex optical coupler 10.
However, because the optical parts such as a star coupler and a wavelength division multiplex optical coupler use an optical fiber for the input/output, radiation loss will occur when bending the optical fiber. In the case of a quarts single mode fiber, the optical fiber has to be bent more than 30 mm of radius of curvature. Furthermore, there is the possibility of the breaking an optical fiber in the case of using the optical fiber strand with 250 xcexcm of outward diameter to save the space for wiring. In the case of using a code with 2 mm to 3 mm of outward diameter to protect the optical fiber, the wiring space will increase because the outward diameter of the code is larger than the outward diameter of the optical fiber strand. Especially, as the number of branching of an optical star coupler is larger, the wiring space has to be larger. Therefore, the conventional art requires the work of packing the optical fiber without breaking it by considering the radius of curvature of the optical fiber.
As stated, it is an object of the present invention to provide a wavelength division multiplex optical star coupler that is capable of solving the problems described above. Also, it is an object of the present invention to provide a communication station and optical transmitting system using the wavelength division multiplex optical star coupler. The object of the present invention can be achieved by the combinations of features described in the independent claims of the present invention. The dependent claims of the present invention define further advantageous embodiments of the present invention.
According to the first aspect of the present invention, a wavelength division multiplex optical star coupler can be provided which comprises an input port which inputs a first optical signal, a first optical coupler which divides the first optical signal input from the input port into a plurality of first optical signals, a plurality of input/output ports, each of which outputs one of the plurality of first optical signals divided by the first optical coupler and inputs a second optical signal, an output port which outputs the second optical signal, and a second optical coupler, provided between the input port and the first optical coupler or between the first optical coupler and the input/output ports, which provides the first optical signal to the input/output ports and the second optical signal to the output port.
A wavelength division multiplex optical star coupler can be provided which further has a plurality of the output ports and a plurality of the second optical couplers, each of which is provided between the first optical coupler and one of the input/output ports. A wavelength division multiplex optical star coupler can be provided such that each of the second optical couplers provides one of the second optical signals to one of the plurality of output ports and each of the plurality of output ports outputs one of the second optical signals.
A wavelength division multiplex optical star coupler can be provided such that the second optical coupler is provided between the input port and the first optical coupler, and the first optical coupler further multiplexes a plurality of the second optical signals and provides the second optical signal to the second optical coupler, and the second optical coupler provides the first optical signal input from the input port to the first optical coupler and provides the second optical signal multiplexed by the first optical coupler to the output port.
A wavelength division multiplex optical star coupler can be provided such that the second optical coupler is a wavelength division multiplex optical coupler that selects an optical signal, a wavelength of which has a prescribed relationship with a wavelength of the second optical signal, from optical signals input to the second optical coupler and outputs the selected optical signal to the output port.
A wavelength division multiplex optical star coupler can be provided such that each of the input port, the input/output port, and the output port has an optical connector adapter that mounts an optical fiber in such a way as capable of attaching and removing the optical fiber.
According to the other aspect of the present invention, a communication station can be provided which comprises an electro-optical converter which inputs an electric signal and converts the electric signal to a first optical signal, a first optical coupler which divides the first optical signal into a plurality of first optical signals, a plurality of input/output ports, each of which outputs one of the plurality of first optical signals divided by the first optical coupler and inputs a second optical signal, an output port which outputs the second optical signal, a second optical coupler, provided between the electro-optical converter and the first optical coupler or between the first optical coupler and the input/output ports, which provides the first optical signal to the input/output ports and the second optical signal to the output port, an opto-electric converter which converts the second optical signal output from the output port to a second electric signal, and an electric signal output terminal which outputs the second electric signal.
A communication station can be provided which further has a plurality of the output ports, a plurality of the second optical couplers, each of which is provided between the first optical coupler and one of the input/output ports, a plurality of the opto-electric converters, each of which is provided for one of a plurality of the output ports, and an electric signal multiplexer which multiplexes a plurality of the second electric signals output from a plurality of the opto-electric converters and outputs the multiplexed second electric signal to the electric signal output terminal.
A communication station can be provided such that each of the second optical couplers provides one of the second optical signals to one of the plurality of output ports, each of the plurality of output ports outputs one of the second optical signals, and each of the plurality of opto-electric converters converts one of the second optical signals to the second electric signal.
A communication station can be provided such that the second optical coupler is provided between the electro-optical converter and the first optical coupler, the first optical coupler further multiplexes a plurality of the second optical signals and provides the second optical signal to the second optical coupler, and the second optical coupler provides the first optical signal input from the electro-optical converter to the first optical coupler and provides the second optical signal multiplexed by the first optical coupler to the output port.
A communication station can be provided such that the second optical coupler is a wavelength division multiplex optical coupler that selects an optical signal, a wavelength of which has a prescribed relationship with a wavelength of the second optical signal, from optical signals input to the second optical coupler and outputs the selected optical signal to the output port.
A communication station can be provided such that each of the input/output port and the output port has an optical connector adapter that mounts an optical fiber in such a way as capable of attaching and removing the optical fiber.
According to the still other aspect of the present invention, an optical transmission system can be provided which comprises a main unit which inputs a first electric signal and outputs a plurality of first optical signals, and inputs a second optical signal and outputs a second electric signal, a plurality of sub units, each of which inputs one of the plurality of first optical signals from the main unit and outputs a third electric signal, and inputs a fourth electric signal and provides the second optical signal to the main unit; and a plurality of optical fibers, each of which connects the main unit and the plurality of sub units.
An optical transmission system can be provided such that the main unit has an electro-optical converter which inputs the first electric signal and converts the first electric signal to a first optical signal, a first optical coupler which divides the first optical signal into a plurality of first optical signals, a plurality of input/output ports, each of which outputs one of the plurality of first optical signals divided by the first optical coupler to one of the sub units through one of the optical fibers and inputs the second optical signal from one of the sub units through one of the optical fibers, an output port which outputs the second optical signal, a second optical coupler, provided between the electro-optical converter and the first optical coupler or between the first optical coupler and the input/output ports, which provides the first optical signal to the input/output ports and the second optical signal to the output port, an opto-electric converter which converts the second optical signal output from the output port to a second electric signal, and an electric signal output terminal which outputs the second electric signal.
An optical transmission system can be provided which further has a plurality of the output ports, a plurality of the second optical couplers, each of which is provided between the first optical coupler and one of the input/output ports, a plurality of the opto-electric converters, each of which is provided for one of a plurality of the output ports, and a electric signal multiplexer which multiplexes a plurality of the second electric signals output from a plurality of the opto-electric converters and outputs the multiplexed second electric signal to the electric signal output terminal.
An optical transmission system can be provided such that each of the second optical couplers provides one of the second optical signals to one of the plurality of output ports, each of the plurality of output ports outputs one of the second optical signals, and each of the opto-electric converters converts one of the second optical signals to the second electric signal.
An optical transmission system can be provided such that the second optical coupler is provided between the electro-optical converter and the first optical coupler, the first optical coupler further multiplexes a plurality of the second optical signals and provides the second optical signal to the second optical coupler, and the second optical coupler provides the first optical signal input from the electro-optical converter to the first optical coupler and provides the second optical signal multiplexed by the first optical coupler to the output port.
An optical transmission system can be provided such that the second optical coupler is a wavelength division multiplex optical coupler that selects an optical signal, a wavelength of which has a prescribed relationship with a wavelength of the second optical signal, from optical signals input to the second optical coupler and outputs the selected optical signal to the output port.
An optical transmission system can be provided such that the sub unit has a sub unit input/output terminal which inputs the first optical signal from the main unit through the optical fiber, an opto-electric converter which inputs the first optical signal and converts the first optical signal to the third electric signal, an antenna which outputs the third electric signal and inputs the fourth electric signal, an electro-optical converter which converts the fourth electric signal to the second optical signal, and a wavelength division multiplex optical coupler which provides the first optical signal to the opto-electric converter and the second optical signal to the sub unit input/output terminal.
An optical transmission system can be provided such that each of the input/output port and the output port has an optical connector adapter that mounts an optical fiber in such a way as capable of attaching and removing the optical fiber.